AT89C51AC2-RLTUM Atmel, AT89C51AC2-RLTUM Datasheet - Page 71

• Manufacturer Part Number: AT89C51AC2-RLTUM
• Description: IC 8051 MCU FLASH 32K 44VQFP
• Manufacturer: Atmel
• Series: 89Cr

Specifications of AT89C51AC2-RLTUM

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 40MHz
• Connectivity: UART/USART
• Peripherals: POR, PWM, WDT
• Number Of I /o: 34
• Program Memory Size: 32KB (32K x 8)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 1.25K x 8
• Voltage - Supply (vcc/vdd): 3 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP, 44-VQFP
• Processor Series: AT89x
• Core: 8051
• Data Bus Width: 8 bit
• Data Ram Size: 1280 B
• Interface Type: UART
• Maximum Clock Frequency: 40 MHz
• Number Of Programmable I/os: 34
• Number Of Timers: 3
• Operating Supply Voltage: 3 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: PK51, CA51, A51, ULINK2
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 10 bit, 8 Channel
• For Use With: AT89OCD-01 - USB EMULATOR FOR AT8XC51 MCU
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Watchdog Timer
Figure 38. Watchdog Timer
4127H–8051–02/08
Fwd Clock
RESET
-
A/T89C51AC2 contains a powerful programmable hardware Watchdog Timer (WDT)
that automatically resets the chip if it software fails to reset the WDT before the selected
time interval has elapsed. It permits large Time-Out ranking from 16ms to 2s @Fosc =
12MHz in X1 mode.
This WDT consists of a 14-bit counter plus a 7-bit programmable counter, a Watchdog
Timer reset register (WDTRST) and a Watchdog Timer programming (WDTPRG) regis-
ter. When exiting reset, the WDT is -by default- disable.
To enable the WDT, the user has to write the sequence 1EH and E1H into WDTRST
register no instruction in between. When the Watchdog Timer is enabled, it will incre-
ment every machine cycle while the oscillator is running and there is no way to disable
the WDT except through reset (either hardware reset or WDT overflow reset). When
WDT overflows, it will generate an output RESET pulse at the RST pin. The RESET
pulse duration is 96xT
should be serviced in those sections of code that will periodically be executed within the
time required to prevent a WDT reset
Note:
-
WDTPRG
-
When the Watchdog is enable it is impossible to change its period.
WDTRST
-
14-bit COUNTER
Enable
-
2
OSC
1
, where T
0
WR
OSC
=1/F
Control
Decoder
OSC
7-bit COUNTER
. To make the best use of the WDT, it
Outputs
A/T89C51AC2
RESET
71